title: Effect of electric arc, gas oxygen torch and induction melting techniques on the marginal accuracy of cast base-metal and noble metal-ceramic crowns.
abstract: OBJECTIVE
  The aim of this study was to identify the most appropriate alloy composition and melting technique by evaluating the marginal accuracy of cast metal-ceramic crowns.
  
  
  METHODS
  Seventy standardised stainless-steel abutments were prepared to receive metal-ceramic crowns and were randomly divided into four alloy groups: Group 1: palladium-gold (Pd-Au), Group 2: nickel-chromium-titanium (Ni-Cr-Ti), Group 3: nickel-chromium (Ni-Cr) and Group 4: titanium (Ti). Groups 1, 2 and 3 were in turn subdivided to be melted and cast using: (a) gas oxygen torch and centrifugal casting machine (TC) or (b) induction and centrifugal casting machine (IC). Group 4 was melted and cast using electric arc and vacuum/pressure machine (EV). All of the metal-ceramic crowns were luted with glass-ionomer cement. The marginal fit was measured under an optical microscope before and after cementation using image analysis software. All data was subjected to two-way analysis of variance (ANOVA). Duncan's multiple range test was run for post-hoc comparisons. The Student's t-test was used to investigate the influence of cementation (α=0.05).
  
  
  RESULTS
  Uncemented Pd-Au/TC samples achieved the best marginal adaptation, while the worst fit corresponded to the luted Ti/EV crowns. Pd-Au/TC, Ni-Cr and Ti restorations demonstrated significantly increased misfit after cementation.
  
  
  CONCLUSIONS
  The Ni-Cr-Ti alloy was the most predictable in terms of differences in misfit when either torch or induction was applied before or after cementation. Cemented titanium crowns exceeded the clinically acceptable limit of 120μm.
  
  
  CONCLUSIONS
  The combination of alloy composition, melting technique, casting method and luting process influences the vertical seal of cast metal-ceramic crowns. An accurate use of the gas oxygen torch may overcome the results attained with the induction system concerning the marginal adaptation of fixed dental prostheses.
authors.affiliation: Department of Buccofacial Prostheses, Faculty of Odontology, Complutense University of Madrid, Spain.
authors.forename: Pablo
authors.initials: P
authors.lastname: Gómez-Cogolludo
authors.forename: Raquel
authors.initials: R
authors.lastname: Castillo-Oyagüe
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Lynch
authors.forename: María-Jesús
authors.initials: MJ
authors.lastname: Suárez-García
mesh_terms: D002484:Cementation / Q000379:methods; D002498:Centrifugation / Q000295:instrumentation; D002858:Chromium Alloys / Q000737:chemistry; D003442:Crowns; D003734:Dental Casting Investment / Q000737:chemistry*; D003735:Dental Casting Technique / Q000295:instrumentation; D018772:Dental Marginal Adaptation; D017267:Dental Prosthesis Design; D005899:Glass Ionomer Cements / Q000737:chemistry; D006047:Gold Alloys / Q000737:chemistry; D007091:Image Processing, Computer-Assisted / Q000379:methods; D016876:Metal Ceramic Alloys / Q000737:chemistry*; D008669:Metallurgy / Q000295:instrumentation / Q000379:methods; D008853:Microscopy; D010165:Palladium / Q000737:chemistry; D011312:Pressure; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry; D014618:Vacuum
chemical_list: D002858:Chromium Alloys; D003734:Dental Casting Investment; D005899:Glass Ionomer Cements; D006047:Gold Alloys; D016876:Metal Ceramic Alloys; D010165:Palladium; D014025:Titanium
keywords: Dental alloy; Gas oxygen torch; Induction; Marginal fit; Pressure-differential casting machine; Vacuum-casting